Interference reduction of multiple signals

ABSTRACT

The present invention reduces the degradation in performance of one or more radio signals that are co-transmitted with a first radio signal from the same transmitting antenna in the same frequency channel and received by the same antenna due to multipath or other shared interference, where the one or more radio signals can be separated from the first radio signal. All received signals are coupled to the same adaptive array or adaptive filter to reduce multipath or other shared interference of the first radio signal, which reduces multipath and other shared interference in the other radio signals before they are separated and processed by their respective receivers, or the individual radio signals are separated before the first signal enters the adaptive array and coupled to a slave weighting network slaved to the weights of the adaptive array of the first signal to reduce interference in all the signals.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.14/269,169, filed May 4, 2014, which is a continuation of U.S.application Ser. No. 14/033,085, filed Sep. 20, 2013, which is acontinuation of U.S. application Ser. No. 13/669,426 (U.S. Pat. No.8,583,068), filed Nov. 5, 2012, which is a continuation of U.S.application Ser. No. 13/227,313 (U.S. Pat. No. 8,311,505), filed Sep. 7,2011, which is a division of U.S. application Ser. No. 12/380,709 (U.S.Pat. No. 8,019,305), filed Mar. 3, 2009, which is a division of U.S.application Ser. No. 11/453,785 (U.S. Pat. No. 7,519,346), filed Jun.15, 2006, which is a continuation of U.S. application Ser. No.10/405,010 (U.S. Pat. No. 7,076,228), filed Mar. 30, 2003, which is acontinuation-in-part of U.S. application Ser. No. 09/438,132 (U.S. Pat.No. 6,564,044), filed Nov. 10, 1999, which claims priority to U.S.provisional application No. 60/108,663, filed Nov. 16, 1998, and theentire contents of each of the above listed applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the use of an adaptive array in radiocommunications and in particular to improve the performance ofcommunications and broadcast systems that incorporate multiple signals.

2. Description of the Prior Art

To obtain high quality reception, communications receivers require asignal that is uncorrupted by interference, such as multipath, adjacentchannel or co-channel. One source of interference that can severelydegrade reception is multipath. Multipath occurs when the transmittedsignal arrives at the receiver's antenna over different propagationpaths resulting in different time delays and phase shifts. The multiplepaths are generally due to reflections of the transmitted signal fromhills, buildings, etc. and can also be the result of atmosphericphenomena. Multipath can cause distortion in the amplitude, phase andfrequency of the received signal, which can result in deep signalstrength fades, frequency selective fades, intersymbol interference,noise, etc.

The same transmitting antenna can be used for the transmission of tworadio communications signals at the same time in the same frequencychannel. At the receiving end, the two radio communications signals canbe received by the same receiving antenna at the same time before beingcoupled to their individual receivers. Both radio signals can sufferfrom interference (multipath and/or other shared interference) problemsand require that the interference be reduced to improve reception.

Two approaches, well known in the art for reducing the effects ofmultipath and other interference, are the adaptive array and adaptivefilter (see for example Widrow, B. & others, “Adaptive Antenna Systems”,Proceedings of the IEEE, Vol. 55, No. 12, December 1967, pp. 2143-2159;Treichler, John R., Johnson, C. Richard Jr., and Larimore, Micheal G.,Theory and Design of Adaptive Filters, John Wiley & Sons, New York,1987; Monzingo, Robert A. and Miller, Thomas W., Introduction toAdaptive Arrays, John Wiley & Sons, New York, 1980; Compton, R. T. Jr.,Adaptive Antenna Concepts and Performance, Prentice Hall, EnglewoodCliffs, N.J., 1988; U.S. Pat. Nos. 4,736,460 and 4,752,969 by KennethRilling, and others). When multiple signals are present, the use of anadaptive array or adaptive filter for each signal can be expensive,complicated and occupy too much space. For some signals, a dedicatedadaptive array or adaptive filter may not provide enough performanceimprovement if the signal structure or available information does notlend itself to the use of an adaptive array or adaptive filter.

SUMMARY OF INVENTION

The present invention reduces the degradation in performance of one ormore radio signals that are co-transmitted with a first radio signalfrom the same transmitting antenna in the same frequency channel andreceived by the same antenna, due to multipath or other sharedinterference, where the one or more radio signals can be separated fromthe first radio signal. All received signals are coupled to the sameadaptive array or adaptive filter to reduce multipath or other sharedinterference of the first radio signal, which reduces multipath andother interference in the other radio signals before they are separatedand processed by their respective receivers, or the individual signalsare separated before the first signal enters the adaptive array oradaptive filter and each of the other signals coupled to an individualassociated adaptive array or adaptive filter slave weighting networkwith weights slaved to the weights of the adaptive array or adaptivefilter of the first signal to reduce the multipath and other sharedinterference in all the signals.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows the prior art simultaneous transmission and reception oftwo signals without multipath present.

FIG. 2 shows the prior art simultaneous transmission and reception oftwo signals with multipath present.

FIG. 3 is a block diagram of the receiving end with an adaptive arraythat reduces multipath in the first and second received signals.

FIG. 4 shows a block diagram of an adaptive filter embodiment of thepresent invention.

FIG. 5 shows block diagram of a prior art CMA adaptive array.

FIG. 6 shows a block diagram using a CMA adaptive array for applicationto an IBOC system for Broadcast FM.

FIG. 7 shows a block diagram showing an adaptive array slave weightnetwork.

FIG. 8 shows a block diagram for the adaptive array for the adaptivearray slave weight network embodiment.

FIG. 9 shows the adaptive array slave weight network 50 for the slaveweight network embodiment.

FIG. 10 shows a block diagram for a digital embodiment.

FIG. 11 shows a software flow block diagram for a digital embodiment.

FIG. 12 shows the prior art simultaneous transmission side usingseparate transmitters for first and second signals before combining.

FIG. 13 shows a block diagram using a CMA adaptive array for applicationto an IBOC system for Broadcast FM with separation of signals implicitin receivers.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The purpose of the present invention is to use one adaptive array toimprove the performance of two receivers by reducing interference(multipath or other interference that is shared) when the two radiosignals occupy the same frequency channel, are transmitted from sameantenna, received by the same antenna or antenna array, and areseparable. In the present invention, interference other than multipathmeans interference shared by both radio signals.

FIG. 1 shows a prior art diagram of the transmission, propagation A, andreception of first and second radio signals. They use the sametransmitter 8A, transmit antenna 10 and receive antenna 24, and occupythe same frequency channel. The signals are generated by the firstsignal generator 2 and second signal generator 4 and coupled to theinputs of signal combiner 6A. The two signals are combined by combiner6A in a manner that permits their separation at the receiver (discussedbelow). They are transmitted by the same transmitter 8A using the sameantenna 10, which gives them the same polarization. They also travelover the same propagation path A and are received by the same antenna24. Bandpass filter 22 selects the frequency channel. If the bandwidthsof the two signals are not so different as to cause significantfrequency dependent propagation or antenna changes, the signals arereceived with the same relative characteristics relative to each otherwith which they were transmitted. The separator 20 at the receivingantenna can then separate the signals and the respective receivers 12and 14 each receive the appropriate signal. For certain types of signalsand conditions, the separator 20 may be implicitly included in thereceivers, as discussed below.

Since the adaptive array can be implemented at baseband, IF or RF, theterm “receiver” refers to the demodulator and receiver output, or theIF, demodulator and receiver output and/or one or RF components (i.e.mixer, bandpass filter, or pre-amp) after the adaptive array, as isappropriate.

FIG. 12 shows the prior art block diagram of the transmission side whichfunctions like the transmission side in FIG. 1 except that the firstsignal and second signal use separate transmitters 8B and 8C,respectively, before being combined by combiner 6B. The output ofcombiner 6B is coupled to antenna 10. For the present invention, antenna10 can be replaced by a dedicated antenna for each transmitter if theantennas locations and characteristics do not significantly change thepath and relative characteristics of the direct path signals or theindirect path signals (discussed below).

FIG. 2 is a prior art diagram of FIG. 1 with multipath. It is the sametransmit and receive configuration as shown in FIG. 1, except thatmultipath is part of the propagation path. FIG. 2 functions in the samemanner as FIG. 1 except the receiving antenna 24 receives first andsecond signal pairs arriving from different directions following pathsA, B, and C. Since the first and second signal pairs are transmitted atthe same time from the same antenna 10 and received by the same antenna24, they will have the same polarization, the same propagation paths A,B, C, and the same changes due to reflections in paths B and C. When thereceiving antenna 24 collects all the multipath components, thecharacteristics of each pair are preserved as if they were transmittedalone (to the first approximation). The signals are then to be separatedby separator 20.

For the case where the first signal is much stronger than the secondsignal, FIG. 3 shows a diagram of the receiving end with an adaptivearray. Both the first and second signals with the associated multipathcomponents are received by the antenna elements 24-1 to 24-N. Eachelement of antenna 24 is individually coupled to the input terminal ofthe associated one of bandpass filter 22-x. The output terminal of eachbandpass filter 22-x is individually coupled to the associated one ofthe input terminals of the adaptive array 30. Adaptive array 30 reducesthe multipath or other interference present in the received signals forthat specific communications system application.

The output terminal of the adaptive array 30 is then coupled to theinput terminal of the separator 20, which separates the first and secondsignals. Separator 20 is discussed below. Output terminals T1 and T2 ofthe separator 20 are coupled respectively to the input terminal ofreceiver 12 and receiver 14 to receive the first and second signalsrespectively.

In some proposed broadcast systems, as discussed below, the first signalis much stronger than the second signal. In FIG. 3, the first signal ismuch strong than the second signal, so that the adaptive array 30responds primarily to the first signal, which controls the adjustmentsof the weights of adaptive array 30 to reject multipath in the firstsignal. Adaptive array 30 is designed to respond to the first signal andits available information (discussed below). The second signal will besubjected to the same weights as the first signal. Since both signalshave the same multipath components, multipath of the second signal willalso be rejected. To use an antenna pattern description, the antennapattern formed by adaptive array 30 to reduce the multipath of the firstsignal is also the antenna pattern required to reduce multipath of thesecond signal because they have similar multipath components. The outputsignal of the adaptive array 30 is separated into the first and secondsignals by the signal separator 20. Receiver 12 receives the firstsignal and receiver 14 receives the second signal. The performance ofboth receivers 12 and 14 are increased by the reduction of multipath andother interference.

In this way the first signal and adaptive array 30 are used to reducemultipath in the second signal. This provides the advantages of usingonly one antenna array and one adaptive array, which reduces costs,number of parts/functions, and space requirements. In cases where theinformation available for the second signal is inadequate or the signalcharacteristics do not permit adequate improvement in the second signalby a dedicated adaptive array, FIG. 3 provides the advantage of betterreceiver performance for the second signal. In general, as a desiredsignal gets weaker, the performance of the adaptive array in rejectinginterference becomes poorer, particularly as the signal strengthapproaches the reception threshold. FIG. 3 has the advantage for thesecond signal in weak signal conditions that the adaptive array forstronger first signal can provide better interference reduction. FIG. 3is a basic embodiment of the present invention.

The first and second signals received by the system of FIG. 3 do notnecessarily have to occupy the same frequency space. They just need tobe in the same frequency channel, as defined by bandpass filter 22 forthe present embodiment of the invention to function. It is not necessaryfor the second signal to occupy the whole channel bandwidthsymmetrically about the center frequency of the channel for the presentinvention to function. For purposes of the present invention, frequencychannel refers to the band occupied by all the significant frequencycomponents defined by the energy mask(s) for that communications orbroadcast system.

When an interference signal other than multipath is received by antennaarray 24 in FIG. 3, adaptive array 30 can remove the interference. Ifthe second signal requires a CMA (constant modulus algorithm) typestandalone adaptive array, an interference signal larger than thedesired signal would capture that CMA adaptive array. The presentinvention can reduce the effects of an interference signal that isstronger than the second signal without the capture problem.

FIG. 3 is only one example of the present invention. The presentinvention includes, but is not restricted to the embodiment in FIG. 3.

If the second signal in FIG. 3 has characteristics similar to the firstsignal, the second signal does not have to be “much weaker” than thefirst signal for the present invention to function because adaptivearray 30 can use the energy in the second signal along with the firstsignal to adapt the weights to the proper values to reduce multipath.

In the case where first signal has a code or training signal that theadaptive array 30 can lock onto, then the power of second radio signaldoesn't have to be much small than the power of the first signal. Thepower level of the second signal is limited to the ability of the firstsignal to lock on the code or training signal in its presence andsuccessfully reduce first signal multipath and other interference.

The separation of the signals does not have to be an explicit separator,such as separator 20 in FIG. 3, it can be implicit in the receiver forsome cases. For example, if the second signal is so much smaller thanthe first signal, the receiver of the first signal can suppress thesecond signal, or if the distortion caused by the second signal is notnoticeable, the second signal does not have to be separated explicitly.A combination explicit separation for one signal and implicit separationthe other signal can be used. Some signals can be both explicitly andimplicitly separable.

The invention represented by FIG. 3 can be implemented at RF, IF, orbaseband. The bandwidths of bandpass filter 22, receiver 12 and receiver14 can be different.

FIG. 4 shows another embodiment of the present invention. FIG. 4 is thesame as FIG. 3 except that the adaptive array 30 is replaced by adaptivefilter 40 and the antenna 24 with N array elements is replaced byantenna 24 with a single element. The antenna 24 in FIG. 4 is coupled tothe input terminal of bandpass filter 22. The output terminal ofbandpass filter 22 is coupled to the input terminal of adaptive filter40. The adaptive filter 40 reduces multipath and other interference.Except for adaptive filter 40 replacing adaptive array 30, FIG. 4 workslike FIG. 3 to reduce multipath and interference in the first and secondsignals.

The present invention can be implemented for more than one processedsecondary signal through the adaptive array or filter controlled by thefirst signal.

FIG. 5 shows a prior art CMA adaptive array 32, which can be used toreduce multipath in FM radio and other type signals (examples in U.S.Pat. Nos. 4,797,950 and 5,608,409 by Kenneth Rilling and Agee, Brian,“The Least-Squares CMA: A New Technique for Rapid Correction of ConstantModulus Signals, ICASSP 86 Proceedings, Vol 2, Pp. 19.2.1-19.2.4). Forbroadcast FM radio, the CMA adaptive array adjusts the weights to reducemultipath.

FIG. 6 shows an embodiment of the present invention which functions likeFIG. 3 for On-Channel, In-Band Digital Audio Radio (IBOC). As found inthe prior art, IBOC has been developed to transmit a digital audio radiosignal in the same allotted frequency space as used by a broadcast FMradio station with the analog FM signal. In some prior art IBOC systems,different types of multi-carrier modulated signals are transmitted withthe analog FM signal with power significantly less than the analog FMsignal, so it does not cause interference with the analog FM signal,etc. (i.e. 25 dB). Multi-carrier modulated signals include orthogonalfrequency division multiplex (OFDM) and spread spectrum multi-carrier.In a recent version of IBOC, the digital signal is an OFDM signal. It isadvantageous to use only one adaptive array at the receiving end toimprove both signals instead of a separate adaptive array for eachsignal for cost and space reasons.

FIG. 6 is like FIG. 3, except that the adaptive array 30 is replaced bya CMA adaptive array 32 that can reduce multipath in an analog FM radiosignal. In an IBOC system, the first signal is the analog FM signal andthe IBOC signal is the second signal. The CMA adaptive array 32 adjustsits weights to reduce multipath by using primarily the analog FM signalbecause it is much stronger than the IBOC signal. CMA adaptive array 32reduces multipath in both the analog FM and the digital signal. Receiver12B is an analog FM receiver for Broadcast FM radio. Receiver 14B is areceiver for IBOC digital signal.

In FIG. 6, if an interference signal (other than multipath), which isstronger than the digital signal but weaker than the analog FM signal,is received, the CMA adaptive array 32 will reject the interferencesignal for both the FM signal and the IBOC signal. This can be a greatadvantage to the digital signal, because a very strong adjacent channelsignal can create interference that is significantly stronger than thedigital signal. Similarly, co-channel interference that is greater thanthe digital signal can occur. FIG. 6 is another embodiment of thepresent invention. The present invention includes, but is not restrictedto the embodiment in FIG. 6.

FIG. 13 shows another embodiment of the present invention where explicitseparation of signals by a separator 20 is not necessary because thereceivers can perform the separation function implicitly. FIG. 13 islike FIG. 6, except that receivers 12B and 14B are replaced by receivers12C and 14C, where receivers 12C and 14C perform the separation functionof separator 20 implicitly. Also, FIG. 13 is different from FIG. 6because the CMA adaptive array output terminal is coupled to the inputterminals of both receivers 12C and 14C, instead of the input terminalof separator 20. Receiver 12C uses the ability of FM to suppressinterference to separate the desired FM signal from the digital signalby viewing the digital signal as a weak interference signal andsuppressing it. Similarly, receiver 14C may view the FM signal as aninterference signal, where the digital signal is a random sequencespread spectrum type multi-carrier signal and receiver 14C appliescorrelation with digital codes to extract the desired digital signal andsuppress the FM signal. The separation here is implicit, and no explicitseparator is needed. The separation is then part of the receiverprocessing. The present invention includes, but is not restricted tothis example of an implicit separator.

In FIG. 7 shows another embodiment of the present invention. The signalsare received at the elements of the antenna array 24, as in FIG. 3. Theinput terminal of each bandpass filter 22-x is coupled the associatedantenna element 24-x. The first input terminal of each mixer 82-x iscoupled to the output terminal of the associated bandpass filter 22-x,and the second input terminal of each mixer 82-x is coupled to theoutput terminal of local oscillator 80 to down convert the receivedsignals of each antenna element 24-x to a convenient frequency at IF.The output terminal of each mixer 82-x is coupled to the input terminalof the associated separator 20B-x, which separates the first signal fromthe second signal. Separator 20B-x separates signals explicitly. Thefirst output terminal of each separator 20B-x is coupled to theassociated input terminal of the adaptive array 34 to deliver theseparated first signal. Adaptive array 34 can be any appropriateadaptive array implementation for the first signal. The second terminalof each separator 20B-x is coupled to the associated input of theadaptive array slave weighting network 50 for the second signal.Adaptive array slave weighting network 50 is discussed below. The slaveweight value output terminals of adaptive array 34, one for each weight,are coupled to the associated slave weight value input terminals ofadaptive array slave weighting network 50. The array output terminal ofadaptive array 34 is coupled to the input terminal of receiver 12 forreceiving the first signal. The output terminal of adaptive array slaveweight network 50 is coupled to input terminal of receiver 14 forreceiving the second signal.

In FIG. 7, the adaptive array 34 reduces the multipath in the firstsignal to improve the performance of the first signal receiver 12. Theweight values generated by the weights of adaptive array 34 are the sameweight values required by the second signal to reduce multipath or otherinterference and are applied to the corresponding slave weights ofadaptive array slave weighting network 50. The weight values of adaptivearray slave weighting network 50 are slaved to the values of theassociated weights of adaptive array 34 (discussed below) to reducemultipath and/or other interference in the second signal. The outputterminal of adaptive array slave weighting network 50 is coupled to theinput terminal of receiver 14 to receive the second signal. Theembodiment of the present invention in FIG. 7 improves the performanceof receiver 14. Since adaptive array 34 is designed to work with thefirst signal, the weights are adjusted to reduce multipath and/or otherinterference in the first signal, which are the weight values to reducemultipath and/or other interference in the second signal via theadaptive array slave weighting network 50. FIG. 7 reduces multipath orother interference in the second signal whether the second signal isstronger or weaker than the first signal.

In the case where separators 20B-x use bandpass and/or bandstopfiltering to separate the first and second signals, not all otherinterference signals are shared by the first and second signals. Sharedother interference signals having the direction of arrival as rejectedmultipath components of the first signal and other interference signalsassociated with the first signal are reduced by the slave weightnetwork.

The present invention can be implemented in FIG. 7 at RF, IF, orbaseband, as appropriate. Similarly, an adaptive filter with receivingantenna 24 with a single element can be used instead of an adaptivearray 34 and a corresponding replacement of adaptive array slaveweighting network 50 with an adaptive filter slave weighting network inFIG. 7 similar to what was shown in FIG. 4.

Equivalent to using only one antenna to transmit both first and secondradio signals is to use two similar antennas that are located closeenough to each other so that there is no significant difference in thetransmission and propagation characteristics of the transmitted radiosignals, just as the two radio signals transmitted from a signal antennadiscussed above. Similarly, two similar receiving antenna arrays locatedclose enough so there is no significant difference in the transmission,propagation and reception characteristics of the first and secondreceived signals is equivalent to the single antenna array discussedabove.

The adaptive arrays 30 and 34 in FIGS. 3 and 7 respectively can be anyadaptive array implementation that can reduce multipath or otherinterference in the first signal with the information available for thespecific application. References given above give examples of adaptivearray and adaptive filter requirements. FIG. 5 gives the CMA adaptivearray 32 that can be used for FM broadcast radio (and other certainmodulation types) to reduce multipath. Similarly, the adaptive filter 40in FIG. 4 is an adaptive filter that is appropriate for the specificapplication for reducing multipath and/or interference with theinformation available for its specific application.

FIG. 8 shows an adaptive array 34. In adaptive array 34, each weightvalue is applied to an associated slave weight output terminal forslaving the associated weights of the adaptive array slave weightnetwork 50. Adaptive array 34 is any adaptive array with linear combinerweight implementation. The N inputs to the adaptive array are coupledthe input terminal of a different one of the N the tapped delay line70-x (two outputs can have an equivalent 90 degree phase shift whenappropriate). Each of the M output terminals of each tapped delay line70-x is coupled to the first input terminal of the associated weight74-yz. The weight value is calculated in weight calculator 78 for eachweight and is applied to the second input terminal of the associatedweight 74-yz and the associated output terminal for each slave weight ofthe adaptive array slave weighting network 50. Each weight 74-yz outputterminal is coupled to a different input terminal-yz of adder 72 to sumthe weighted signals. The output terminal of adder 72 is coupled toreceiver 12 and weight calculator 78.

Similarly, an adaptive filter embodiment of the present invention isidentical to adaptive filter 40 in FIG. 4 except the value of eachweight is applied to an associated slave weight output terminal to slavethe associated weight of the adaptive filter slave weight network.

FIG. 9 shows the adaptive array slave weight network 50, which is theslave weight counterpart of adaptive array 34. The first input terminalof each weight 76-yz is coupled to the second output terminal of theassociated separator 20-x in FIG. 7. The second input terminal of eachweight 76-yz is coupled to the output terminal of the associated slaveweight output terminal of adaptive array 34 in FIG. 7 to control theweight value. The output signal of each weight 76-yz is coupled to aninput terminal of adder 72 that adds all the weighted signals. Theoutput terminal yz of adder 72 is coupled to the input terminal ofreceiver 14.

The weights of the adaptive array 34 and associated adaptive array slaveweights of network 50 includes, but are not restricted to linearcombiner forms of weights. In FIG. 7 the weight structure of adaptivearray slave weighting network 50 mirrors the weight structure of theassociated adaptive array 34.

The adaptive filter slave weight network is similar to the adaptivearray slave weight network and mirrors the structure of the associatedadaptive filter 40.

In signal combiner 6A and 6B of FIGS. 1, 2 and 12, the first, second,etc. signals are combined in such a way that they can be separated atthe receiving end by separators 20, 20A, or implicitly in the receivers,which compliments the combining technique of signal combiners 6A and 6B.Various techniques can be used. Some examples which are well known inthe art are as follows: 1) Two signals can be combined in quaderature.The quaderature characteristics are then exploited at the receiving endto separate the two signals. 2) The signals can occupy differentfrequency bands in the channel. Frequency band selective filters canseparate the signals at the receiving end. 3) Random sequences can beapplied to each signal before combining so that the signals are spread,and correlation of the each random sequence is applied at the receivingend to extract the signals, as found in the spread spectrum prior art.4) Two signals can be combined in a way that the receiver of the firstsignal suppresses the second signal without having to explicitly removethe second signal. For example, a strong first signal that is FM cansuppress a much weaker second signal without explicitly removing thesecond signal. Similarly, if the weak second signal is a spread spectrumsignal, the second receiver can pull the second signal out withoutexplicitly separating the first signal if it can achieve lock.Combinations of the methods can also be used. The present inventionincludes, but is not restricted to these examples of combining methodsand separation methods of signals.

The receivers 12, 14, etc. are receivers that extract the intelligenceof the received signals that are appropriate for each signal.

When multipath is present, this invention applies only to those adaptivearray and multiple signal applications where the same weight values andassociated antenna pattern of the adaptive array is appropriate forrejecting multipath interference for all the signals of interest.

It would be clear to a person skilled in the art that the presentinvention can be implemented in analog, digital, analog/digital hybrid,software/digital, etc., also as partially illustrated below.

FIG. 10 shows the present invention implemented with the use of acomputer, microprocessor, or digital signal processors (DSP) 110. Theembodiment of the present invention in FIG. 10 and the correspondingsoftware flow diagram in FIG. 11 are similar to those found in U.S. Pat.No. 5,608,409 by Kenneth Rilling, except the input data that it operateson contains representations of the first and second radio signals.

As in the analog embodiments of the present invention, the first signal,second signal, multipath signals and other interference signals arereceived by the N elements of antenna 24 with each antenna elementcoupled to the input terminal of a corresponding bandpass filter 22 x.In turn, the output terminal of each bandpass filter 22-x is coupled tothe first input terminal of a corresponding mixer 82-x. The second inputterminal of each mixer 82-x is coupled to output terminal of localoscillator 80. The output terminal of each mixer 82-x is subsequentlycoupled to a corresponding input terminal of detector network 70 and theinput terminal of a corresponding analog-to-digital (A/D) converter100-x, where the output port of each A/D converter in turn is coupled tothe corresponding input port of computer/microprocessor/DSP 110. Theoutput terminal of detector network 70 is coupled to the input terminalof A/D converter 101, the output port of which is in turn is coupled tothe corresponding input port of computer/microprocessor/DSP 110. Theadaptive array algorithm for a specific embodiment of the presentinvention is implemented in the computer/microprocessor/DSP 110, anexample of which is discussed below. The output port ofcomputer/microprocessor/DSP 110 is coupled to the input port of D/Aconverter 105 to convert the digital representation of the adaptivearray output signal to an analog signal. The output terminal of D/Aconverter 105 is coupled to the input terminal of separator 20. Thefirst and second output terminals of separator 20 are coupled to theinput terminals of receivers 12 and 14 respectively to receive the firstand second signals respectively.

FIG. 11 shows a flow chart for a software embodiment of the adaptivearray of the present invention shown in FIG. 6 which is a specificconstant modulus implementation of the adaptive array algorithm tocompute each weight value, however, the software embodiment of thepresent invention is not limited to the embodiment presented below. Themathematical relationships for implementing the software is given inU.S. Pat. No. 5,608,409 by Kenneth F. Rilling where they are explainedand discussed. At least one software embodiment is possible for each ofthe various embodiments of the present invention provided above.

In FIG. 11, each of the digitized antenna element signals from A/Dconverters 100-x goes to splitter/delayer block 125. Thesplitter/delayer block 125 makes M copies (one for each adaptive loop)of the incoming data from each A/D converter 100-x, delaying each of theM copies an appropriate length of time such that it functions as thesoftware equivalent of an M output tapped delay line. Thesplitter/delayer block 125 output goes to loop input limiting block 128and weighting block 126.

Loop input limiting block 128 computes the input signal level (i.e.envelope) for each antenna element and then computes the amplitudelimited signal for each adaptive loop by applying the followingcalculation:L _(i)(n)=X _(i)(n)/|X _(i)(n)|  eq (1)where i refers to the “i”th adaptive loop, n refers to the “n”th timesample, and X, the input signal of the ith loop. The output of loopinput limiting block 128 goes to the correlation multiplier block 122.

Weighting block 126 weights each adaptive loop input signal, startingwith an initial weighting value, by making the following calculation foreach adaptive loop:S _(i)(n)=X _(i)(n)*W _(i)(n)  eq (2)where W_(i) is the weight of the “i”th adaptive loop. The output ofweighting block 126 goes to the summing block 130.

Summing block 130 sums the weighted values of all the input signals ofall the adaptive loops using the following calculation:S _(t)(n)=ΣS _(i)(n)  eq (3)

The output data of summing block 130 goes to feedback limiting block140. The output of summing block 130 also provides the output signal ofthe adaptive array which can be used in its digital form in a digitalreceiver, etc. or be applied to a digital-to-analog converter, asappropriate.

Feedback limiting block 140 computes the adaptive array output signallevel and then the amplitude limited version of the adaptive arrayoutput signal, as follows:ε(n)=S _(t)(n)/|S _(t)(n)|  eq (4)The output data of feedback limiting block 140 goes to the gain controlblock 160.

The gain control block 160 computes the amplitude of the feedback signalusing the following equation:ε_(c)(n)=α*D(n)*ε(n)  eq (5)where D(n) is the gain of gain control block 160 as determined by theinput signal level of the adaptive array, detector network 70 (FIG. 10),and gain control block 160, and α is a constant. The output of gaincontrol block 160 goes to correlation multiplying block 122.

Correlating multiplier block 122 multiplies the amplitude limited inputfor each adaptive loop calculated in the loop input limiting block 128with the feedback signal as follows:M _(i)(n)=ε_(c)(n)*L _(i)(n)  eq (6)

The output of correlation multiplying block 122 is applied to weightcalculating block 124 which computes the next weighting value for eachweight using the following equation:W _(i)(n+1)=W _(i)(n)+M _(i)(n)  eq (7)where this new value of each weight is used to update each weight valuefor calculation of the next data sample. This process continues for eachsuccessive data sample with the weights converging to steady statevalues.

AGLC 11J (described in U.S. Pat. No. 5,608,409 by Kenneth Rilling) ismade up of detector network 70 and A/D converter 101 in FIG. 10 and gaincontrol block 160 in FIG. 11. This software embodiment of the presentinvention in FIGS. 10 and 11 functions in a manner similar to its analogcounter part in FIG. 6.

The computer, microprocessor, or digital signal processors (DSP) 110,software design, A/D converters 100 and 101 in FIG. 10, and anyassociated digital-to-analog converter for the adaptive array outputsignal are chosen so that they can function in real time for thespecific adaptive array application to which it is applied.

This is only one example software/digital embodiment of the presentinvention. The present invention includes, but is not restricted to thisexample.

From the foregoing description, it will be apparent that the inventiondisclosed herein provides novel and advantageous performanceimprovements for receiving separable signals which are transmitted fromthe same antenna and received by the same antenna for the adaptivearray. It will be understood by those familiar with the art, theinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof.

What is claimed:
 1. A method for use in an adaptive filter, the methodcomprising: a) generating, for an input signal, one or more shiftedoutput signals, the shifted output signals including respective timedelay shifts or respective phase shifts, each time delay shift being atleast zero, each phase shift magnitude being at least zero, the inputsignal being derived from K received signals that were each transmittedseparately from a different one of K transmit antennas at a commontransmitter end, each of the K transmitted signals having been formed bytransmitting a different representation of a common signal in a commonfrequency channel, the common signal being made up of an at least onefirst signal and an at least one second signal, the K transmittedsignals being other than spread spectrum signals, wherein K is at least2, and b) generating an adder output signal that is a function of thesum of the products of i) each of the shifted output signals with ii) arespective one of a plurality of weights associated with that shiftedoutput signal, the plurality of weights being determined in such a wayas to reduce interference in a particular type of signal that theadaptive filter was designed to process.
 2. A method as in claim 1,wherein the at least one first signal and the at least one second signalof the common signal are such that each one of the at least one firstsignal and the at least one second signal can be separately derived fromthe adder output signal.
 3. A method as in claim 1, further comprising:repetitively performing steps a) and b); and repetitively determiningeach one of the plurality of weights based on i) the associated shiftedoutput signal, and ii) the adder output signal, the determining of theplurality of weights being such that the plurality of weights convergeto substantially a steady state.
 4. A method as in claim 1, wherein therepresentations of the at least one first signal and the at least onesecond signal of the common signal were transmitted at the same time. 5.A method as in claim 1, wherein the determining of the plurality ofweights is carried out based on propagation characteristics of at leastone of the first signals of the representations of the at least onefirst signal of the common signal.
 6. A method as in claim 1, whereinthe K received signals include at least one training signal, so that thedetermining of the plurality of weights is carried out based on at leastone of the at least one training signal.
 7. A method as in claim 1,wherein each one of the representations of the at least one first signalof the common signal includes at least one training signal, so that thedetermining of the plurality of weights is carried out based on one ormore training signals of at least one of the at least one trainingsignals.
 8. A method as in claim 1, wherein the common signal is atleast part of a multi-carrier signal.
 9. A method as in claim 8, whereinthe multi-carrier signal includes an orthogonal frequency divisionmultiplex signal.
 10. A method as in claim 1, wherein the adaptivefilter includes a digital processor, and wherein at least thedetermining of the plurality of weights is carried out using the digitalprocessor.
 11. A method as in claim 1, wherein each of the plurality ofweights is an analog weight.
 12. A method for use in an adaptive filter,the method comprising: a) generating, for an input signal, an associatedone or more shifted output signals, the shifted output signals includingrespective time delay shifts or respective phase shifts, each time delayshift being at least zero, each phase shift magnitude being at leastzero, the input signal being derived from two received signals that wereeach transmitted separately from a different one of two transmitantennas at a common transmitter end, the two transmitted signals havingbeen formed by transmitting separately a one A first signal and zero ormore A second signals from one antenna and a one B first signal and atleast one B second signal from the other antenna that are in a commonfrequency channel, and b) generating at least two adder output signalsthat are each separately a function of a separate sum of the associatedproducts of i) each of the associated shifted output signals of thatadder output signal with ii) a respective one of a plurality of weightsassociated with that shifted output signal, the plurality of weightsbeing determined in such a way as to reduce interference in a particulartype of signal that the adaptive filter was designed to process, thezero or one A second signal and the at least one B second signal aresimilar enough to the one A first signal and the one B first signal sothat the one A second signal and the at least one B second signal areused with the one A first signal and the one B first signal in thedetermining of the plurality of weights.
 13. A method as in claim 12,wherein the determining of the plurality of weights is carried out basedon propagation characteristics of the one A first signal and the one Bfirst signal.
 14. A method as in claim 12, wherein the two receivedsignals each include at least one training signal, so that thedetermining of the plurality of weights is carried out based on at leastone of each one of the at least one training signals.
 15. A method as inclaim 12, wherein the one A first signal and the one B first signal eachinclude at least one training signal, so that the determining of theplurality of weights is carried out based on at least one of each of theat least one training signals.
 16. A method as in claim 12, wherein theone A first signal, the zero or more A second signals, the one B firstsignal, and the at least one B second signal are at least part of amulticarrier signal.
 17. A method as in claim 16, wherein themulti-carrier signal includes an orthogonal frequency division multiplexsignal.
 18. A method as in claim 12, wherein each of the plurality ofweights is an analog weight.
 19. A method for use in an adaptive filter,the method comprising: a) generating, for an input signal, a firstseparated signal and a second separated signal, the first separatedsignal representing an A first signal and a B first signal and thesecond separated signal representing zero or more A second signals andone or more B second signals of the two received signals, the inputsignal being derived from the two received signals, the two receivedsignals were each transmitted separately from a different one of twotransmit antennas at a common transmitter end, the two transmittedsignals having been formed by transmitting the A first signal and thezero or more A second signals from one of the two transmit antennas andtransmitting the B first signal and the one or more B second signalsfrom the other one of the two transmit antennas that are in a commonfrequency channel, b) generating a first adder output signal that is afunction of the sum of the products of i) each of a representation ofthe first separated signal and a representation of the second separatedsignal with ii) a respective one of a plurality of first weightsassociated with that one of the representation of the first separatedsignal and the representation of the second separated signal, theplurality of first weights being determined in such a way as to reduceassociated interference in a particular type of signal that the adaptivefilter was designed to process, the zero or more A second signals andone or more B second signals are similar enough to the A first signaland the B first signal so that the zero or more A second signals and oneor more B second signals are used with the A first signal and the Bfirst signal in the determining of the plurality of first weights, andc) generating a second adder output signal that is a function of the sumof the products of i) each of the representation of the first separatedsignal and the representation of the second separated signal with ii) arespective one of a plurality of second weights associated with that oneof the representation of the first separated signal and therepresentation of the second separated signal, each one of the pluralityof second weights is derived from an associated one of the plurality offirst weights.